The art of VLBI scheduling

Very Long Baseline Interferometry (VLBI) is a truly global scientific effort that demands rigorous coordination among a network of telescopes distributed worldwide. Central to this collaboration is the generation and distribution of a synchronized observation plan, a task typically called scheduling. Given a network of telescopes, a catalog of celestial sources, and a constrained time window, the goal of scheduling is to find an optimal sequence of observations to achieve the best possible scientific outcomes.

The complexity of this task arises from the virtually infinite number of potential schedules, making it practically impossible to find the most perfect solution. Instead, the objective is to generate a schedule that balances quality with practical constraints. Additionally, numerous optimization criteria must be considered, such as maximizing the number of observations for increased redundancy, ensuring a well-distributed coverage in azimuth and elevation angles to mitigate atmospheric effects, and achieving a balanced distribution of observations across the network and sources to enhance the parameter estimation process. Unfortunately, many of these criteria are in direct conflict with each other, further complicating the optimization process.

However, the importance of optimized scheduling cannot be overstated, as it directly determines the data available for analysis and, consequently, the quality of the scientific results. In recent years, significant progress has been made in VLBI scheduling algorithms. State-of-the-art practices involve generating hundreds of potential schedules for each experiment and using simulations to evaluate and select the optimal one. Nowadays, developing advanced scheduling algorithms requires a multifaceted approach, encompassing the creation of logical observation sequences, the generation of high-quality simulations, and the application of cutting-edge analysis and parameter estimation techniques. Additionally, new observing scenarios emerging from upcoming satellite missions, e.g. Genesis, combined with the more interdisciplinary application of VLBI resources, are fundamentally changing scheduling optimization objectives.

In this lecture, I will give a brief introduction to VLBI scheduling, highlighting its unique and exciting challenges. I will discuss recent advancements in scheduling algorithms and their impact on VLBI science. Furthermore, I will provide insights into future challenges and opportunities.